Artificial snow making method and product for implementing the method

ABSTRACT

Disclosed is a snow making method incorporating nucleation agent particles into water and in spraying the water containing the nucleation agent particles onto a surface or into an ambiance whose temperature is lower than 0° C., by way of a device for producing snow or ice. The nucleation agent particles consist in silicate particles whose unit equivalent spherical diameter is lower than 15 μm, and preferably lower than 5 μm. Also disclosed is the powdery product for implementing the method.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to the field of artificial snow making.

More particularly, it relates to a snow making method consisting inincorporating nucleation agent particles into water and in spraying saidwater containing said nucleation agent particles into an ambiance whosetemperature is lower than 0° C., by means of a device for producingsnow.

The invention also relates to a particular product, in powder form,intended to be incorporated into water to serve as a nucleation agentwithin the framework of the implementation of the above-mentioned snowmaking method.

It also relates to the use of a powdery product to serve as a nucleationagent within the framework of the implementation of the snow makingmethod.

Description of the Related Art

Generally, it is known to make artificial snow, in particular on skislopes, in order to compensate for the lack of natural snow.

Artificial snow is made by means of snow production devices (also called“snowmakers”), supplied via pressurized water, and possibly pressurizedair, ducts.

Such devices spray water into the cold ambient air as droplets thatfreeze or crystallize to produce snow.

The possibilities of producing snow, as well as the quality of the snowproduced, depend on the atmospheric conditions present.

Generally, the colder the ambient air, the easier it is to produce goodquality artificial snow. As a corollary, it is not easy to produce asnow of quality in quite common conditions of negative temperature closeto 0° C.

The snow production devices may comprise a pole firmly fixed in theground, which carries, via distinct supply ducts, pressurized water andpressurised air to a snowing head located at its free end, severalmeters or even about ten meters high.

The snowing head often comprises a plurality of spray nozzles, whosepressurized water and pressurized air supply are adjusted via one orseveral valves, so as to optimize the quantity of artificial snow to beproduced as a function of the weather conditions.

Snow production devices are also known, which comprise water spraynozzles associated with a fan structure whose air flow is adapted toensure the dispersion into the ambient air of the water dropletsproduced.

In both cases, if only this water spraying is used, the drops do notfreeze in flight but only when they touch the ground, hence creating anice sheet.

This is due to the so-called “supercooling” phenomenon, that preventsthe natural freezing of pure water before several tens of degreesCelsius under zero.

Hence, it has been demonstrated that, to make the water freeze atrelatively high temperatures, it is necessary to initiate the process bymeans of one or several foreign bodies, called “nucleation agent(s)”.

For that purpose, it is common to inject ice nuclei into the main jet ofthe above-mentioned snow making devices, by means of one or severaldevices called “nucleators” associated with the water spray nozzles.

This method is efficient but it requires producing cold, generally by aviolent expansion of pressurized air, and it hence consumes high energy.The impact on the cost of a snowing installation is hence significant.

It is also possible to perform the nucleation by applying shocks on thewater, in particular through ultrasounds.

However, the corresponding devices are complex and also consume a lot ofenergy; moreover, without pressurized air, the nucleation agents are notwell distributed in the jet and the required power becomes higher thanthat required for a nucleation by conventional compressed air.

The document U.S. Pat. No. 4,200,228 proposes another solution toincrease the temperature from which the snow production devices may beimplemented in good conditions and produce snow without pressurized air.

For that purpose, it is provided to incorporate into water particlesacting as nucleation agents, which are in the form of fragments of cellsderived from microorganisms and containing a protein capable ofinitiating the crystallization, when this water is sprayed into the airas fine droplets.

The corresponding product, in powder form, is marketed by SNOMAXCompany, under the name SNOMAX (registered trademark).

This product acts under −2.8° C. and it is the better industrialnucleation agent produced to date.

Its presence has also other virtues, as that to make the snow more easyto work and hence to save snow grooming time.

However, the production of this biological product for making artificialsnow is quite expensive.

Moreover, it requires particular cold storage conditions, and itsimplementation requires a binding operating procedure taking intoaccount its biological nature.

Other higher performance nucleation agents exist, for example themetaldehyde, active at −0.4° C., but they are unusable in the context ofsnow production, in particular due to their toxicity.

There hence exists a need to propose a new type of nucleation agent formaking artificial snow, which is cheap, easy to implement and lowpolluting.

SUMMARY OF THE INVENTION

In order to remedy the above-mentioned drawback of the state of the art,the present invention proposes a snow making method consisting inincorporating nucleation agent particles into water and in spraying saidwater containing said nucleation agent particles onto a surface or intoan ambiance whose temperature is lower than 0° C. (advantageously, anambiance whose temperature is comprised between −4° C. and −0.5° C.), bymeans of a device for producing snow or ice; this method beingcharacterized in that said nucleation agent particles consist insilicate particles whose unit equivalent spherical diameter is lowerthan 15 μm, and preferably lower than 5 μm.

According to another feature, at least 10% of said silicate particlesinclude at least one micro-cavity open by a surface aperture anddelimited by a lateral wall defining the inner volume thereof, said atleast one micro-cavity being adapted to initiate the birth or thegeneration of ice in its inner volume when said water spraying is madeinto an ambiance whose temperature is comprised between −4° C. and −0.5°C.

Advantageously, the method consists in using a base of silicateparticles, in which base at least 80% of the particles have a unitequivalent spherical diameter lower than 15 μm, and preferably lowerthan 5 μm.

By “equivalent spherical diameter”, it is meant the diameter of a spherehaving the same volume as that of a nucleation agent particle.

Interesting results have been obtained with silicate particles chosenamong the group consisted of the feldspars, tectosilicates, inosilicatesand phyllosilicates. In particular, the silicate is advantageously afeldspar of the microcline type and/or a feldspar of the orthoclasetype.

It has hence been possible in particular to crystallize water dropletson a cold plate above −2.8° C. and up to −0.3° C.

According to other non-limitative and advantageously features of themethod, taken individually or according to all the technically possiblecombinations:

-   -   for making snow, the silicate particles are incorporated into        the water in a number comprised between 5×10⁵ and 2×10¹⁰        particles per litre of water, preferably between 5×10⁵ and 7×10⁸        particles per litre of water;    -   said spraying of the water containing said silicate particles        consists in spraying the water in the form of droplets whose        size is comprised between 100 and 700 μm;    -   the silicate particles are incorporated into the water so as to        obtain between one silicate particle for 10 water droplets and        ten silicate particles per water droplet.

Still preferably, the method according to the invention provides tosubject said particles to at least one activation treatment before theirincorporation into water, said at least one activation treatment beingadapted to make micro-cavities on the surface of said particles, makingit possible to increase the temperature at which said particles are ableto initiate the formation of ice.

This making of micro-cavities (or pores, or orifices) may consist,either in creating micro-cavities that didn't exist before the treatmentapplied, or in uncovering (or revealing) pre-existing micro-cavitiesthat were previously at least partially closed.

The micro-cavity(ies) in question are open by a surface aperture andthey are delimited by a lateral wall, the depth thereof beingadvantageously greater than the diameter of the disk equivalent to thesurface of said surface aperture (called equivalent diameter).

Within this framework, one or several of the following treatments areadvantageously applied:

-   -   applying to the previously water impregnated particles at least        one cold treatment, and preferably at least two successive cold        treatments, separated by a warming phase.

Said cold treatment(s) then advantageously consist in cooling theparticles down to under −7° C. during at least 10 minutes, then warmingthem up to above 0° C. during at least 10 minutes.

-   -   immersing said particles into an aqueous solution of potash;        said activation treatment then advantageously comprises the step        consisting in immersing said particles into an aqueous solution        of potash during at least 20 minutes and at a temperature        comprised between 0° C. and 90° C.    -   applying to the particles a step of ultrasound cleaning and        separation of said particles;        said ultrasound treatment step is advantageously performed in        aqueous medium before one of the above-mentioned treatments.    -   exposing said particles to an ozone atmosphere in a suitable        reactor, preferably during at least 20 minutes, at a temperature        comprised between 0° C. and 300° C.    -   exposing said particles to an oxygen plasma in a suitable        reactor, preferably during at least 10 minutes, at a temperature        comprised between 0° C. and 300° C.

The invention also proposes a powdery product consisted of silicateparticles whose unit equivalent spherical diameter is lower than 15 μm,wherein said product is intended to be incorporated into water to serveas a nucleation agent within the framework of the above-mentioned snowor ice making method.

In this product, preferably, at least 10% of the silicate particlesinclude at least one micro-cavity open by a surface aperture anddelimited by a lateral wall; still preferably, the depth of said atleast one micro-cavity is greater than the equivalent diameter of itssurface aperture.

This surface aperture of said at least one micro-cavity has preferablyan equivalent diameter comprised between 100 and 1000 nm and a depthcomprised between 700 nm and 3 μm.

The invention still proposes the use of such a powdery product to serveas a nucleation agent within the framework of the implementation of theabove-described artificial snow making method.

In the following description:

FIG. 1 is a curve which shows the freezing temperature of a same drop(Tfdrop(° C.)) placed on a plate of Amazonite, as a function of thenumber of freezing/melting cycles (whose protocol is detailedhereinafter in the description);

FIGS. 2a and 2b correspond to two pictures taken with an electronmicroscope, showing the effect of the freezing of a water drop put onthe surface of a thin plate of Amazonite; FIG. 2a shows the state ofsurface before the water freezing and FIG. 2b shows the state of surfaceafter the freezing;

FIGS. 3 to 6 are pictures under an electron microscope which illustratein four steps the generation of ice in the inner volume ofmicro-cavities on a Microcline plate;

FIGS. 7 and 8 are pictures taken with an electron microscope, which showthe state of surface of a Microcline plate, respectively before andafter an oxygen plasma treatment, according to a first magnifying power;

FIGS. 9 and 10 are pictures taken with an electron microscope, whichshow the state of surface of the same Microcline plate as FIGS. 7 and 8,still respectively before and after the oxygen plasma treatment,according to a second magnifying power, higher than the first one;

FIG. 11 are curves which show the effect of an oxygen plasma treatmenton the freezing temperature of a set of water drops deposited on a plateof Microcline;

FIG. 12 are curves which show the effect of a potash treatment on thefreezing temperature of a set of water drops containing Microcline inpowder deposited on a glass slide;

FIG. 13 are curves which show the effect of ozone and sonicationtreatments on the freezing temperature of a set of water dropscontaining Microcline powder.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

To obtain silicate particles, rock blocks are used, of the typeadvantageously chosen among the group consisted of the feldspars,tectosilicates, inosilicates and phyllosilicates, which are dry crushedby means of a crusher (for example, a jaw crusher or a pebble mill),until obtaining a powder of particles at least 80% of which have a unitequivalent spherical diameter lower than 15 μm, preferably lower than 5μm.

For example, at least 80% of the particles obtained have a unitequivalent spherical diameter comprised between 1 and 7 μm.

One or several treatments can be applied to the particles during orafter the crushing.

These treatments may be intended to:

-   -   sort the particles by size,    -   select the most active particles,    -   improve the activity of the particles.        Tests Illustrating the Efficiency of a Material on the        Crystallization Initiation

As the full-scale tests of the efficiency of a nucleation agent are longand expensive to implement, the inventors have used a known method,implementable in laboratory, based on the cooling down of a plate orblade and the observation at small scale of the temperature at which thecrystallization of a calibrated water drop is initiated.

Protocol #1:

A thin plate, or blade, of the silicate material to be tested isprepared, whose thickness is of the order on 0.5 to 1 mm and on whichhas been deposited a drop of distilled water.

This preparation is placed on a cooling system of the Peltier platetype, whose temperature is controlled to within a tenth of degreesbetween −20° C. and +20° C. (Peltier cooling plate of the Linkam type,with an accuracy of 0.1° C.).

The system is placed in a closed environment in controlled conditions ofhumidity to avoid any condensation.

The temperature is rapidly lowered down to a few degrees above 0° C.,and then slowly (of the order of 1° C./min) while visually evaluatingthe freezing of the drops with an optical microscope.

And the temperature at which the freezing starts for each droplet isrecorded.

For this protocol #1, as the temperature of the drops is higher than thetemperature of the Peltier plate, the temperatures measured on thePeltier plate must be increased by a certain value to obtain the desirednucleation temperature.

The exact difference is previously calibrated by means of a thermocouplesensor introduced into the drop.

Protocol #2:

The silicate powder as prepared hereinabove is used and put insuspension into distilled water at the volume concentration of the orderof 0.01% to 1%.

Drops of such a suspension are deposited on a support glass slide, ofthe type conventionally used in microscopy and the inert aspect thereofon the nucleation is previously checked.

The so-prepared glass slide is placed on a cooling system of the Peltierplate type, whose temperature is controlled to within a tenth of degreesbetween −20° C. and +20° C. (Peltier cooling plate of the Linkam type,with an accuracy of 0.1° C.).

The system is placed in a closed environment in controlled conditions ofhumidity to avoid any condensation.

The temperature is rapidly lowered down to a few degrees above 0° C.,and then slowly (of the order of 1° C./min) while visually evaluatingthe freezing of the drops with an optical microscope.

And the temperature at which the freezing starts for each droplet isrecorded.

It will be noted that the higher the freezing temperature the more thedroplets remain transparent, which make the detection by other means, inparticular automatic means, very uncertain.

For this protocol #2, as the temperature of the drops is higher than thetemperature of the Peltier plate, the temperatures measured on thePeltier plate must be increased by a value of the order of 1.5° C. toobtain the desired nucleation temperature.

Results:

Many tests have been carried out to test silicate particles, accordingto the above-mentioned protocol #2, whose results are given in thefollowing Tables 1 and 2 (divided into two sections for a betterreadability).

TABLE 1 Temp. Maxi Temp. Mini Average Temp. Sample Mineral Source Family(°) (° C.) (° C.) Snomax Reference Snomax Bio −2.5 −5.5 −2.9 AZ-B1Amazonite Brasil-Minas Gerais Tectosilicate −1.5 −11.5 −4.5 AZ-K1Amazonite Russie-Kola Tectosilicate −1.5 −7.5 −3.8 OM1 MicroclineMalawi-Mt Malosa Tectosilicate −0.5 −6.7 −2.6 IFK1 MicroclineInde-Rajahstan Tectosilicate −1.3 −13.5 −4.4 IF8 MicroclineInde-Rajahstan Tectosilicate −1 −14.8 −3.9 ORI1 OrthoclaseInde-Rajahstan Tectosilicate −2 −13 −4.3 ORP Orthoclase MadagascarTectosilicate −1.5 −10 −2.8 AEG1 Aegyrine Malawi-Mt Malosa Inosilicate−1.4 −7.5 −4.1 Thor Thorite USA-El Paso NM Nesosilicate −2.5 −6.2 −3.6IF5 K-Mca Espagne Phyllosilicate −3 −14.5 −6.9

TABLE 2 Sample Number of experiences % Very High temp. % High temp.Snomax 28 86% 96% AZ-B1 17 65% 71% AZ-K1 11 55% 73% OM1 124 80% 92% IFK1144 40% 69% IF8 146 65% 78% ORI1 29 52% 83% ORP 58 38% 66% AEG1 44 57%84% Thor 21 76% 90% IF5 46 22% 30%

In the following of this text, it will be talked about very highcrystallization temperatures when they are higher than or equal to −3°C. and high crystallization temperatures when they are between −4° C.and −3° C.

For the different samples referenced, these tables 1 and 2 mention themineral type, the origin thereof (source), the family thereof, themaximum and minimum crystallization temperatures obtained, the number ofexperiences performed, the percentage of very high crystallizationtemperatures obtained and the percentage of high crystallizationtemperatures obtained.

As the better nucleation agent known is the SNOMAX product (registeredtrademark), the nucleation temperature of this agent on a glass slide isthe reference to which the different products are compared in all theresults.

A first series of tests on the SNOMAX product (registered trademark) hasmade possible to film the different phases of the freezing of a drop andto calibrate the nucleation temperatures.

From a first series of coarsely crushed minerals, it has been found thata particular feldspar: the amazonite (ref. AZ-B1) had as goodperformances as the SNOMAX product (registered trademark).

However, these performances appeared only after several freezing/meltingcycles, as shown in the curve of FIG. 1.

This curve of FIG. 1 shows the freezing temperature of a same drop(Tf_(drop)(° C.)) placed on a plate of Amazonite ref. AZ-B1 (accordingto the above-mentioned protocol #1), as a function of the number offreezing/melting cycles (whose protocol is detailed hereinafter in thedescription).

In this figure, it can be observed that the crystallization temperature,initially −6.2° C., get better as a function of the number of freezingcycles, to arrive at −2.5° C. after 15 cycles.

To understand this phenomenon, thin plates or blades of amazonite havebeen cut to implement the above-mentioned protocol #1. The observationof the drop crystallization under an optical microscope has shown thatthe ice came from under the surface of the plate when the nucleationtemperature was the highest.

The same observations have been made under an electron microscope; a mapof the nucleation sites has been made, and the only remarkable elementhighlighted was the presence of surface micro-cavities, at which the icecrystals appeared.

Moreover, the application of one or several freezing/melting cyclesturned out to make appear microcracks and new micro-cavities.

FIGS. 2a and 2b correspond to two pictures taken with an electronmicroscope, showing the effect of the freezing of a water drop put onthe surface of a thin plate of material ref. AZ-B1.

FIG. 2a shows the state of surface before the water freezing and FIG. 2bshows the state of surface after the freezing.

At the circled places that correspond to the same surface zones, it isclearly seen in white (after freezing) new, very thin cracks,accompanied with new holes (in black); in FIG. 2b , at the bottom right,the cracks initiate the detachment of a grain of material of 2 μm.

On the other hand, it has been remarked that the disappearance of themicro-cavities was associated with a lowering of the nucleationtemperature.

The amazonite having the drawback to be a semi-precious stone, othermicrocline feldspars have been tested, whose high-temperature operationappeared similar and even better than the amazonite.

This is the case, in particular, of a microcline coming from MontMalosa, in Malawi, referenced OM1 in the tests.

Indeed, with this variety, it had been possible to crystallize the waterat −0.5° C., and that, from the first freezing.

However, the source of this mineral is difficult and there exists noexploitable feldspar mine in the region.

It has been highlighted that this mineral has many surfacemicro-cavities open by a surface aperture and delimited by a lateralwall that defines the inner volume thereof. As the repeatability isremarkable, it has been possible to photography under an electronmicroscope, in presence of water steam, the birth or the generation ofice in the inner volume of these micro-cavities on a microcline plate,ref. OM1.

This birth of ice is illustrated in four steps by the pictures of theappended FIGS. 3 to 6.

Other varieties (ref. IFK1 and IF8), coming from known mines inRajahstan, India, require several freezing before reaching their bestnucleation temperatures.

In the case of these 2 microclines acting at very high temperatures(ref. IFK1 and IF8), the presence of micro-cavities has been observedand is at the origin of the nucleation of a part of the nucleationzones.

These “active” micro-cavities have been characterized, under amicroscope, by their depth that is greater than the greatest dimensionof their surface aperture, and preferably by their depth greater than orequal to the equivalent diameter of their aperture surface.

Tests on particles (grains) of material have shown that the higher thenumber of such micro-cavities the higher the number of active grains atvery high temperatures.

By widening the search to other feldspars, it has been highlighted thatseveral orthoclases have a relatively high nucleation temperature,including 2 very high ones, comparable to the microclines.

One of them comes from India (ref. ORI1) and the other one fromMadagascar (ref. ORP).

By further widening the search, the inventors have found 2 mineralswithout any relation with the feldspars that also act at hightemperature: the Aegyrine (ref. AEG1) and the Thorite (ref. Thor).

Although they have no possible direct application in snowing, theseminerals show that the high-temperature nucleation capacity is notlimited to the feldspars and that the phenomenon is wider. This is thecase, for example, of certain potassic micas (ref. K-Mica).

It has also been highlighted that not all the microclines operate athigh temperatures and that other varieties have nucleation temperaturescomparable to the poorer microclines.

By examining the Thorite sample under an electron microscope,micro-cavities of great depth with respect to the equivalent diameter oftheir surface aperture have been highlighted, a characteristic thathence appears as essential to the nucleation in the silicates.

This characteristic may hence be retained for the choice by the oneskilled in the art of the base material to be used, for the preparationof active particles as a nucleation agent in the production ofartificial snow.

Without this can be deduced from any theory, the particular containmentof the water perhaps allows the ice to be formed and to reach thecritical size at very high temperature, then to extend out of themicro-cavity, and that up to several degrees above the surfacenucleation temperature.

The number of active grains as a function of the crushing is also animportant parameter because, for a mineral powder added in water to beeconomically viable, the quantity thereof must not be too high.

In theory, just one particle per drop is sufficient to perform thenucleation. In practice, taking into account the interactions betweendrops, it is not necessary that all the drops contain a particle. Oneparticle for 10 drops turns out to be enough.

On the other hand, the size of this particle must not exceed 15 μm forit to remain in suspension in the drop of size comprised between 100 and500 μm during its time of flight. And it must not be lower than 2 μm tohave at least one micro-cavity.

We then arrive to quantities of mineral of the order of 100 g to 2 kgfor 380 m³ of water.

It is understood that, for a culture snow application, the proportion ofactive grains at very high temperature is essential.

Within this framework, to improve the nucleation temperature and toincrease the number of active grains, the inventors had the idea toattempt to create new micro-cavities on the material particles, or tofree (or “clean”) the existing micro-cavities from a part at least ofthe materiel liable to clog them.

For that purpose, different treatments turned out to be interesting:

-   -   the cold treatment (for creating new micro-cavities), and    -   the ultrasound (sonication), potash, ozone and/or oxygen plasma        treatments (for cleaning the micro-cavities).        Treatment(s) for Activation of the Silicate Particle Powder        A/ Cold Treatments:

The powder coming from the crushing is mixed with water and subjected toone or several freezing cycles.

The mixture is frozen either by aspersion onto a cold surface, ormassively in a suitable container.

The freezing temperature TC is lowered down under −7° C.; thetemperature lowering is made from the ambient temperature, at a speed of1 to 20° C./minute.

After freezing, the mixture is maintained at the temperature TC duringat least 10 minutes.

The mixture is then unfrozen at a temperature TD comprised between +0.1°C. and +4° C.

Once the mixture totally unfrozen, after 10 minutes, another cycle canbegin.

Between 1 and 15 cycles can be carried out that way.

At the end of the last cycle, the powder is extracted from the mixture,for example by filtration, then dried.

It has been observed that this treatment causes the creation of newactive micro-cavities (whose depth is higher than the equivalentdiameter of their surface aperture) and FIG. 1 shows the efficiency ofsuch a treatment on the increase of the nucleation temperature.

As mentioned hereinabove, the curve of FIG. 1 shows the freezingtemperature of a same drop placed on a plate of Amazonite ref. AZ-B1(according to the above-mentioned protocol #1), as a function of thenumber of freezing/melting cycles.

It is observed that the first freezing occurs at −6.2° C., that after 7cycles it increases to −3.1° C. to reach a maximum of −2.5° C. after 15cycles.

B/ Oxygen Plasma Treatment:

The powder is rinsed out with pure water then fully dried.

A second drying is performed with dry nitrogen.

Spreading out the powder as a thin layer onto an inert substrate (forexample, a silica glass plate).

Putting the plate covered with powder into an hermetic chamber.

Closing the chamber and vacuuming the latter (air pressure lower than 20mbar).

Filling the chamber with dioxygen up to a pressure of about 200 mbar.

Operating the plasma generator during 20 to 30 minutes.

Restoring the atmospheric pressure and stirring the powder.

Repeating the cycle 2 or 3 times.

Tests of efficiency of this oxygen plasma treatment have been carriedout on plates of silicate ref. OM1, according to protocol #1.

FIGS. 7 and 8 are pictures taken with an electron microscope, which showthe state of surface of the corresponding plate before and after theoxygen plasma treatment, according to a first magnifying power; andFIGS. 9 and 10 are pictures taken with an electron microscope, whichshow the state of surface of the same plate, still before and after theoxygen plasma treatment, according to a second magnifying power, higherthan the first one.

It is then observed a greater number of micro-cavities on the surface ofFIG. 8 with respect to that of FIG. 7.

On the other hand, FIG. 10 shows the disappearance of debris orparticles from the micro-cavities with respect to FIG. 9 and also thepresence of sharper angles.

FIG. 11 shows the effect of the oxygen plasma treatment on the freezingtemperature of a set of water drops deposited on a plate of silicateref. IFK1, according to protocol #1.

The ordinate axis represents the cumulated percentage of frozen drops.

The abscissa axis represents the temperature of the water in the drop.

On this graph, it is observed that, before treatment (curve IFK1), 40%of the drops freeze above −3° C., whereas 100% of the drops are frozenat −3° C. after the oxygen plasma treatment (curve IFK1 PLASMA).

C/ Potash Treatment:

The powder coming from the crushing is mixed with a solution ofpotassium hydroxide having a concentration between 10 and 100% during 20to 60 minutes.

Then, it is washed with pure water so that the pH comes back under 8.

Thereafter, the powder may be dried or kept in water.

Many tests have been carried out on the same minerals, without and withthe hereinabove potash treatment.

Without the potash treatment, the nucleation has been obtained at veryhigh temperature in 37% of the cases, and at high temperature in 53% ofthe cases.

Whereas with the potash treatment, the nucleation has been obtained atvery high temperature in 63% of the cases and at high temperature in 48%of the cases.

FIG. 12 shows the effect of the 10%-potash treatment on the freezingtemperature of a set of water drops containing IFK1 in powder (particleslower than 15 μm) deposited on a glass slide and tested according toprotocol #2 (curve IFK1 KOH).

By comparison, the curve of manually-crushed IFK1 immediately before thetest (curve fresh IFK1) is shown.

The ordinate axis represents the cumulated percentage of frozen drops.

The abscissa axis represents the temperature of the water in the drop.

It is observed that, before the treatment, less than 30% of the dropsfreeze above −3° C., whereas more than 60% of the drops are frozen above−3° C. after the potash treatment.

It is also to be noted that 100% of the drops are frozen at −5° C. afterthe treatment, whereas it is necessary to reach −8° C. to obtain thisresult with the raw product freshly crushed.

D/ Ozone Treatment:

The powder is rinsed out with pure water then fully dried.

A second drying is performed with dry nitrogen.

Spreading out the powder as a thin layer onto an inert substrate (forexample, a silica glass plate).

Putting the plate covered with powder into a chamber.

Closing the chamber and filling it with dioxygen.

Circulating the dioxygen during at least 5 minutes.

Lighting the ultraviolet lamp that transforms the dioxygen into ozone.

Leaving the powder exposed to ozone during 20 to 30 minutes.

Switching off the lamp and opening the chamber.

Rinsing out the powder with pure water.

Optionally, drying it out.

Optionally, performing the cycle several times.

Results showing the efficiency of this ozone treatment appear on theappended FIG. 13, commented hereinafter.

E/ Ultrasound Treatment (Sonication):

The micro-cavities tend to become naturally clogged; in particular,during the crushing, the thinner particles adhere to the surfaces andclog the pores. The impurities present during the different steps forobtaining the product may also play the same role. These impurities areoften organic. The use of ultrasounds allows unsticking a potentialbiofilm or grains retained by surface effect and breaking certainimpurities.

Treatment Applied:

The raw or water-mixed powder is placed in a container, itself immersedinto a ultrasound tank.

The tank operates with a 40 kHz-frequency generator and the exposurelasts at least 10 minutes.

A variant consists in immersing an ultrasound generator into the powdercontainer.

Results showing the efficiency of this ultrasound treatment appear inFIG. 13 shown hereinafter.

FIG. 13 shows the effect of the ozone and sonication treatments on thefreezing temperature of a set of water drops (Tdrop(° C.)) containingIFK-1 powder, tested individually according to protocol #2.

The same batch of IFK1 powder has been used for the 4 series of tests.

The ordinate axis represents the cumulated percentage of frozen drops.

The abscissa axis represents the temperature of the water in the drop.

In FIG. 13:

-   -   the curve “raw IFK1” illustrates the results obtained without        treatment,    -   the curve “IFK1 US” illustrates the results obtained with the        ultrasound treatment (sonication),    -   the curve “IFK1 O3 20 min.” illustrates the results obtained        with an ozone treatment (during 20 minutes), and    -   the curve “IFK1 US+O3” illustrates the results obtained with a        ultrasound treatment followed with an ozone treatment.

The different effects of the ozone treatment (O3), of the sonication(US) and of both combined can be observed

It is observed that the first drops containing non-treated powder ofIFK1 freeze at −5.7° C. and represent only 12% of the drops. To have100% of frozen drops, it is necessary to go down to a temperature of−8.9° C.

The sonication treatment (IFK1 US) improves the temperature of firstfreezing and the percentage of frozen drops at the highest temperaturebecause 32% of the drops are frozen at −3.7° C. It will also be notedthat 100% of the drops are frozen at −5.2° C.

The ozone treatment alone (IFK1 O3) still improves the freezingtemperature of the first drops: 17% are frozen as soon as −2.7° C. 100%of the drops are frozen at −7.3° C., which is better than the rawproduct but poorer than the sonication treatment.

By combining both treatments, a high increase of the number of activegrains at high temperature is obtained because 60% of the drops arefrozen at −3.7° C. and 100% at −5.2° C.

It will be noted that the different treatments mentioned hereinabove maybe implemented in isolation or in combination. In particular, asonication treatment is advantageously implemented before any othertreatment.

Operating Mode for Producing Artificial Snow

The silicate particles, preferably activated by one or several of theabove-mentioned treatments, are incorporated into the supply water ofthe snowmakers, in a number comprised between 5×10⁵ and 2×10¹⁰ particlesper litre of water, preferably between 5×10⁵ and 7×10⁸ particles perlitre of water, so as to obtain between one silicate particle for 10water droplets and ten silicate particles per water droplet, knowingthat the desired size of droplets to be produced is comprised between100 and 700 μm.

The spraying of the droplets into the ambient air for making snow iscarried out by any known artificial snow production device.

As variant, a part of the snow production device in contact with thewater flow may be made of silicate, said water flow then picking up therequired quantity of particles by erosion.

Such a method may also serve in making ice, for example in an ice rinkor in a crushed ice production machine by spraying water containing thenucleation agent as silicate particles against a cold surface(temperature lower than or equal to 0° C.). In these cases, the highnucleation temperature allows using higher temperatures of water, andhence of coolant, and hence improving the efficiency.

The invention claimed is:
 1. A snow making method comprising: subjectingnucleation agent particles to at least one activation treatment, saidnucleation agent particles consisting of silicate particles having aunit equivalent spherical diameter lower than 15 μm, said at least oneactivation treatment creating at least one micro-cavity on the surfaceof said nucleation agent particles; incorporating the nucleation agentparticles into water after subjecting the nucleation agent particles tothe at least one activation treatment; and spraying said watercontaining said nucleation agent particles onto a surface or into anambiance having a temperature lower than 0° C., by a device configuredto provide snow or ice.
 2. The method according to claim 1, wherein theunit equivalent spherical diameter of the silicate particles is lowerthan 5 μm.
 3. The method according to claim 1, further comprising usinga base of silicate particles, at least 80% of the silicate particles inthe base having a unit equivalent spherical diameter lower than 15 μm.4. The method according to claim 1, wherein the silicate particles arechosen from the group consisting of feldspars, tectosilicates,inosilicates, and phyllosilicates.
 5. The method according to claim 4,wherein the silicate particles are one or more of: (i) a microclinefeldspar and (ii) an orthoclase feldspar.
 6. The method according toclaim 1, wherein the silicate particles are incorporated into the waterin a number comprised between 5×10⁵ and 2×10¹⁰ particles per liter ofwater.
 7. The method according to claim 1, wherein said spraying of thewater containing said silicate particles includes spraying the water inthe form of droplets having a size comprised between 100 and 700 μm. 8.The method according to claim 7, wherein the silicate particles areincorporated into the water to obtain between one silicate particle for10 water droplets and ten silicate particles per water droplet.
 9. Themethod according to claim 1, wherein the temperature of the ambianceinto which the water spraying occurs is comprised between −4° C. and−0.5° C.
 10. The method according to claim 1, wherein said micro-cavityis open by a surface aperture and is delimited by a lateral wall, thedepth of said at least one micro-cavity being greater than the diameterof the disk equivalent to the surface of said surface aperture.
 11. Themethod according to claim 1, wherein said at least one activationtreatment includes applying at least one cold treatment to thepreviously water-impregnated particles.
 12. The method according toclaim 11, wherein said at least one activation treatment includesapplying at least two successive cold treatments, separated by a warmingphase, to the previously water-impregnated particles.
 13. The methodaccording to claim 11, wherein said at least one cold treatment includescooling the particles down to under −7° C. during at least 10 minutes,followed with a warming up to above 0° C. during at least 10 minutes.14. The method according to claim 1, wherein said at least oneactivation treatment includes exposing said particles to an ozoneatmosphere in a reactor, at a temperature comprised between 0° C. and300° C.
 15. The method according to claim 1, wherein said at least oneactivation treatment includes exposing said particles to an oxygenplasma in a reactor, at a temperature comprised between 0° C. and 300°C.
 16. The method according to claim 1, wherein said at least oneactivation treatment includes immersing said nucleation agent particlesinto an aqueous solution of potash.
 17. The method according to claim16, wherein said nucleation agent particles are immersed into theaqueous solution of potash during at least 20 minutes and at atemperature comprised between 0° C. and 90° C.
 18. The method accordingto claim 1, wherein said at least one activation treatment includesultrasound cleaning and separation of said nucleation agent particles.19. The method according to claim 18, wherein said ultrasound cleaningis performed in aqueous medium.